1. Field of the Invention
In recent years, there have been an increasing number of demands for reduction in size, weight, and thickness of electronic circuit devices incorporated into electronic equipment, such as a portable phone. For this purpose, a technique of mounting high-density thin electronic components, such as large scale integrated circuits (hereinafter referred to as LSIs), has been proposed.
2. Background Art
For example, Japanese Patent Unexamined Publication No. 2000-340607 is disclosed. FIGS. 5A–5C are sectional views showing major steps of manufacturing a conventional electronic circuit device. The conventional electronic circuit device is structured so that electrodes (not shown) on circuit board 41 are connected to corresponding connection terminals (not shown) on LSI 42 via solder bumps 43.
A method of manufacturing the conventional electronic circuit device is described with reference to FIGS. 5A–5C.
First, as shown in FIG. 5A, a plurality of solder bumps 43 are formed on the electrodes on circuit board 41.
Next, as shown in FIG. 5B, adhesive sheet 45, including thermoplastic polyimide resin and having cylindrical holes 44, is bonded to LSI 42. At this time, the adhesive sheet is bonded to the LSI so that cylindrical holes 44 through adhesive sheet 45 correspond to the connection terminals provided on LSI 42.
Next, as shown FIG. 5C, solder bumps 43 formed on circuit board 41 are fitted into corresponding cylindrical holes 44 through adhesive sheet 45. Further, circuit board 41 and LSI 42 are pressed and heated to at least a melting temperature of solder bumps 43. Then melting of solder bumps 43 connects the connection terminals on LSI 42 and corresponding electrodes on circuit board 41. At the same time, bonding circuit board 41 and LSI 42 via adhesive sheet 45, softened by heating, forms an electronic circuit device.
However, in the conventional electronic circuit device, solder having a melting point of at least 200° C. is used as an electrically connecting material; thus, an inexpensive general-purpose polymeric resin sheet having a low heat-resistant temperature cannot be used as substrate material of a circuit board. Therefore, because expensive substrate material having a high heat-resistant temperature, e.g. epoxy resin including glass fiber or a ceramic plate, is used, there is a problem of an expensive electronic circuit device.
Further, there is another problem. When the adhesive sheet is heated to bond the LSI and circuit board, air may be mixed into the adhesive sheet, or melted solder may diffuse into adjacent bumps, thus decreasing insulation resistance. For this reason, it is difficult to manufacture highly reliable electronic circuit devices with high yields.